is it possible to check a 3 phase contactor on resistance to earth with no power to it but all 3 phases connected?

install monkey

23-09-2011, 09:36 PM

contactors only fault on coil burn out,contacts welded,or 2 phasing,or melt from loose connection causing excessive heat.
u can test the component ie compressor or fan from the outgoing side of the contactor,but this doesnt eliminate the cable from being at fault,best to disconnect the comp,motor and test at the terminals,also you can inspect the terminals

andyc425

23-09-2011, 09:52 PM

basically came to a job had a p8 fault on a daikin which is an outdoor fault ,condenser was not running i checked 3 phases coming into isolator and found that i had lost one phase, i confirmed this by checking contact coming on off main supply and 1 32 amp fuse had blown.to identify what caused this i checked compressor windings all ok resistance to earth on fan motors all ok,i did notice fuse which protects 240 v circuit was not sitting flush in it holding which would indicate if it was something on the 240 circuit it would have bypassed the fuse and blown secondary on main supply.In summary i was unable to check condenser contact but foolishly checked resistance to earth with 3 phases connected with no power

install monkey

23-09-2011, 10:00 PM

p8 is a mitsi fault, if the compressor siezes it will trip on the thermal overload,if its dte then it will blow 2 phases.
the control fuse is normally fed of red phase.check for loose connections on the isolator. isnt the cond fans powered off the control fuse. check the supply cable from isolator to cond terminals,see if its rubbed and shorted against pipework or casing!!

basically came to a job had a p8 fault on a daikin which is an outdoor fault ,condenser was not running i checked 3 phases coming into isolator and found that i had lost one phase, i confirmed this by checking contact coming on off main supply and 1 32 amp fuse had blown.to identify what caused this i checked compressor windings all ok resistance to earth on fan motors all ok,i did notice fuse which protects 240 v circuit was not sitting flush in it holding which would indicate if it was something on the 240 circuit it would have bypassed the fuse and blown secondary on main supply.In summary i was unable to check condenser contact but foolishly checked resistance to earth with 3 phases connected with no power

chillerman2006

23-09-2011, 10:12 PM

something much bigger will be feeling resistance to earth shortly

that satelite !! :D thats about to crash in to our atnosphere

R's chillerman

Tayters

23-09-2011, 10:26 PM

is it possible to check a 3 phase contactor on resistance to earth with no power to it but all 3 phases connected?

Hi Andy,

Do you mean meggering the compressor from the outgoing terminals on the contactor? If so then it would work as long as nothing else comes off the outgoing terminals (i.e. thay go straight to the compressor) to power something that might not like a good meggering.

Otherwise if you megger the incoming part of the contactor with the outdoor isolator off the you'll be checking any part of that cabling (Between isolator and incoming feed to contactor) to earth which no doubt will go through some control circuits which wont take it well.